1. Field of the Invention
The present invention relates to the field of powertrain control systems for hybrid powertrain configurations. In particular, the present invention includes a system and method for controlling the idle speed of a hybrid powertrain utilizing the torque from one or both of an internal combustion engine and an electric motor-generator.
2. Description of the Related Art
Hybrid vehicles generally consist of series hybrid vehicles, powersplit hybrid vehicles, and parallel hybrid vehicles. Parallel hybrid vehicles usually include at least a internal combustion engine and a motor-generator disposed along a vehicle powertrain such that the torques produced by each drive means are effectively summed together to drive ,the vehicle. A typical hybrid vehicle is usually driven directly by the mechanical output of the internal combustion engine. However, when the vehicle must be accelerated or decelerated at a rate that cannot be accomplished by the internal combustion engine alone or if the drive efficiency of the engine would be degraded if only the internal combustion engine were used, the motor-generator, which is mechanically connected to the powertrain, operates as an electric motor (during acceleration) or as an electric generator (during deceleration) to compensate for the limitations or inefficiencies of the internal combustion engine.
In a hybrid vehicle the motor-generator can provide rapid acceleration or deceleration. Fluctuation in the internal combustion engine""s speed can be suppressed, and thus the hybrid vehicle provides the advantages of reduced fuel consumption and reduced emissions. Since the consumption of the internal combustion engine can be regulated as desired, the hybrid vehicle can be low-noise, low-emission and low-fuel consumption vehicle. For example, the hybrid vehicle can be driven by only the motor-generator even if the internal combustion engine is stopped, since both the internal combustion engine and the motor-generator are selectively mechanically connected to the driving wheels. The motor can also quickly start and stop the internal combustion engine, further increasing fuel economy.
A problem that arises in a typical hybrid vehicle occurs when the vehicle is in an idle state, i.e. the torque provided by the respective powertrain components is not being transferred to the drive wheels. Nevertheless, any hybrid powertrain must operate in a neutral, speed control mode for various purposes including powering accessories, recharging batteries, or warming up the internal combustion engine and exhaust aftertreatment system, or meeting other requirements. A specific control system for controlling the idle speed of a hybrid powertrain is therefore desirable.
Generic drive control systems exist for hybrid vehicles. For example, one drive control system discloses an apparatus and method for limiting the usage of the internal combustion engine such that the necessary torque is generated, the fuel consumption of the vehicle is maximized, and the undesirable emissions from the vehicle are minimized. The aforementioned system, however, does not disclose a control system for specifically controlling the performance of the hybrid powertrain when the powertrain is in an idle model
Accordingly, the present invention provides an apparatus and a method for controlling the idle speed .of a powertrain. The present invention receives information about the state of the Starting/Lighting/ignition (SLI) 12 V battery and the High Voltage (HV) battery, and demands from accessories like air conditioning to determine which of several idle speed control modes the powertrain should operate within, and then executes that control strategy.
The possible idle speed control operating modes detailed are (1) engine-torque-control/motor-speed-control, (2) engine-off/motor-speed-control, and (3) engine-speed-control/motor-torque-control. Note that the mode engine-speed-control/motor-off is assumed to be a special case of (3) above wherein the desired motor torque is zero, meaning that the motor is switched off.
The engine-off/motor-speed-control mode is used when all conditions to turn the engine off (such as catalytic converter temperature, engine temperature, battery state of charge, etc) are met. The motor is run at a speed that is determined by the ancillary demandsxe2x80x94subject to motor or engine constraints.
The engine-torque-control/motor-speed-control operating mode is used when the engine is required to be on to provide torque to various mechanically driven ancillary loads, or to charge the batteries. The engine torque is set to meet the requirements and demands, and the fast response of the motor in speed-control mode is used to keep the engine at idle speed. Note that if the engine runs smoother under heavy load, then the engine idle speed may be lowered. This instance may occur, for example, if the motor is generating power into the battery.
The engine-speed-control/motor-torque-control operating mode is used when the engine is required to be on because of conditions not related to providing torque to other components. Using this scheme, the engine is set into idle-speed control mode, and the motor is used to provide fast transient responses to keep the idle speed smooth, and to keep the engine slightly under load for xe2x80x9copportunisticxe2x80x9d charging and to allow the engine to operate at a lower idle speed and more smoothly.